In LTE (Long Term Evolution) that is used as the next-generation mobile communication specification, the uplink radio access scheme adopts SC-FDMA (Single Carrier-Frequency Division Multiple Access) while the downlink radio access scheme employs OFDMA (Orthogonal Frequency Division Multiple Access).
OFDMA is a digital modulation and demodulation scheme in which a plurality of carrier waves (called sub-carriers) are multiplexed using orthogonality between frequencies. Accordingly, OFDMA is said to have robust resistance to fading and multi-path interference.
On the other hand, the characteristic of SC-FDMA is similar to OFDMA. The different point of SC-FDMA from OFDMA is that sub-carriers allocated to the users are continuous. Accordingly, SC-FDMA is expected to be enhanced in power efficiency compared to OFDMA. The uplink radio resources provided in LTE are divided into frequency and temporal components. The divided resources are allocated to users, or specifically, to mobile terminals.
FIG. 1 is an illustrative diagram showing a radio frame, slots and RBs (Resource Blocks) in LTE. One RB is composed of 12 sub-carriers. There exist 100 RBs in a 20 MHz system. There exist 50 RBs in a 10 MHz system. There exist 25 RBs in a 5 MHz system.
The radio base station generally uses PF (Proportional Fair) scheduling as the radio resource allocating method (see Patent Document 1).
As described in Patent Document 1, in PF scheduling, the fairness between the throughput per cell and the throughput between mobile terminals are taken into consideration.
According to PF scheduling, the radio base station, first, calculates for every mobile terminal, the ratio between the average throughput of the mobile terminal and the feasible throughput of the mobile terminal, calculated from the radio condition at the point where the mobile terminal is located. The radio base station compares the ratio with others, and allocates radio resources to the mobile terminals that have not been preferentially allocated with radio resources in the past when the radio condition is fine.
Selection index M of each mobile terminal in PF scheduling is given as follows, using average throughput X(n) of the mobile terminal at the present point of time n and the feasible throughput R(n) of the mobile terminal under the radio conditions that exist at the point where the mobile terminal at the present point of time n is located:
                              M          ⁡                      (            n            )                          =                              R            ⁡                          (              n              )                                            X            ⁡                          (              n              )                                                          [                  Math          ⁢                                          ⁢          1                ]            
Here, as M(n) of a mobile terminal is greater, the mobile terminal is more likely to be allocated with radio resources.
Specifically, on the uplink the radio base station calculates the SINR (Signal to Interference and Noise power Ratio) for the SRS (Sounding Reference Signal) included in the received data from a mobile terminal. The radio base station, based on the result (SINR), estimates the throughput R that the mobile terminal can realize under the radio condition at the point where the mobile terminal is located.
On the other hand, on the downlink the radio base station, using the CQI (Channel Quality Indicator) reported from the mobile terminal, estimates the throughput R that the mobile terminal can realize under the radio conditions that exist at the point where the mobile terminal is located.
Further, when allocation of radio resources to the mobile terminal is made, the radio base station calculates:
                              X          ⁡                      (                          n              +              1                        )                          =                                            (                              1                -                                  1                  T                                            )                        ⁢                          X              ⁡                              (                n                )                                              +                                    1              T                        ⁢                          R              ⁡                              (                n                )                                                                        [                  Math          ⁢                                          ⁢          2                ]            
to compute the average throughput X of the mobile terminal.
On the other hand, when RB allocation has not been made, the radio base station calculates:
                              X          ⁡                      (                          n              +              1                        )                          =                              (                          1              -                              1                T                                      )                    ⁢                      X            ⁡                          (              n              )                                                          [                  Math          ⁢                                          ⁢          3                ]            
to compute the average throughput X of the mobile terminal. Here, T represents the average window size.
Patent Document 2 discloses a mobile communication system that performs PF scheduling by taking into account the traffic at the base station.
In this mobile communication system, the mobile terminal selects a radio base station by taking into account the traffic at the radio base station. The mobile terminal transmits the throughput DRC (predictive data communication speed) which the terminal can realize under the radio conditions that exist at the point where the terminal is located. The radio base station calculates a selection index M for each of the mobile terminals that have transmitted DRC to the base station. Based on each selection index M, the radio base station selects mobile terminals to which radio resources should be allocated.
Patent Document 3 discloses a packet transmission control apparatus that can realize various schedulers including a Max C/I (Maximum C/I) scheduler, PF scheduler, M-LWDF (Modified Largest Weighted Delay First) scheduler, etc., by implementation of a calculation program of one evaluation function.
In a Max C/I scheduler, the selection index M of the mobile terminal is calculated using an equation M=R. This equation, i.e., M=R is the calculation formula of the selection index M used in the PF scheduler from which the average throughput X of the mobile terminal is left out.
In a M-LWDF scheduler, the resident time of a packet in the radio base station and the service priority are incorporated in the calculation formula of the selection index M used in a PF scheduler.